This invention relates to a vacuum toilet system with simultaneous rinse and discharge.
It has for many years been conventional to use recirculating toilet systems in aircraft because a relatively large amount of liquid is required to transport the waste material in a gravity toilet system, and by recirculating the liquid the total quantity of liquid required to operate the system is reduced. Recirculating toilet systems are subject to the disadvantage that the recirculating liquids that they employ are corrosive, and therefore leakage from a recirculating toilet system may enable the corrosive liquid to contact structural members of the aircraft, resulting in the structural integrity of the aircraft being impaired.
Vacuum toilet systems have been known for many years. The modern vacuum toilet system comprises a waste-receiving bowl, a sewer pipe that can be placed under a pressure that is substantially lower than that in the interior of the waste-receiving bowl, and a discharge valve for controlling passage of material from the waste-receiving bowl into the sewer pipe. When the discharge valve is opened, material in the waste-receiving bowl is transported into the sewer pipe by virtue of the pressure difference between the interior of the waste-receiving bowl and the interior of the sewer pipe. The system also comprises a source of rinse liquid and a rinse liquid valve for controlling introduction of rinse liquid into the waste-receiving bowl.
Vacuum toilet systems do not lend themselves to recirculation, because of the large pressure difference between the downstream side of the discharge valve and the upstream side of the rinse liquid valve. However, because vacuum toilet systems rely on vacuum for removal of the waste material from the bowl, the amount of rinse liquid that is needed in the vacuum toilet system is much smaller than the amount of rinse liquid required in a gravity toilet system. Consequently, non-recirculating vacuum toilet systems employing water as rinse liquid are attractive for use in aircraft.
Use of vacuum toilet systems is not confined to aircraft, and vacuum toilet systems are used aboard other transport vehicles, such as ships, buses and trains. Vacuum toilet systems have also found use in stationary installations.
A problem with conventional vacuum toilet systems, particularly those aboard passenger vehicles, is that of noise generated when the discharge valve is opened and air rushes at high speed into the sewer pipe.
U.S. Pat. No. 4,713,847 issued Dec. 22, 1987, the disclosure of which is hereby incorporated by reference herein, describes a vacuum toilet system designed for use aboard aircraft. In a practical implementation of that system, the rinse water valve is opened in response to actuation of a flush button, and the rinse water valve remains open for approximately 0.7 s and then closes. About 0.3 s later, the discharge valve begins to open, allowing the contents of the toilet bowl to be removed. The discharge valve takes about 0.5 s to open, remains open for about 3 s and then takes about 0.5 s to close. This sequence of operations was adopted in order to be sure there was time for the rinse water to clean waste material from the side of the bowl before the discharge valve is opened, and to provide a pool of water in the bottom of the bowl in order to reduce the level of noise when the discharge valve opened. In addition, by opening the valves sequentially, the peak current required by the installation is minimized.
In a known vacuum toilet system designed for use aboard a ship, the rinse liquid valve opens, before the discharge valve opens, remains open while the discharge valve is open, and closes after the discharge valve has closed. In this system, minimizing the quantity of rinse liquid is not a major objective.